@1338-bang ,
What part of “text editor” makes you think “background image”?
There are two interpretations I can see of what you are asking, so the next two paragraphs will reply to those interpretations.
#1: How to see a background image in Notepad++? Notepad++ is a text editor, not a page layout program. Even if you did convince Notepad++ to show a background image, it would only be for your copy of Notepad++, and not for anyone else using NPP or any other text editor, because text files have no concept of a background image.
#2: How to get background image in HTML using Notepad++? If you are editing HTML or similar text-based code in Notepad++, that’s something you can do. And if you are asking how to implement a background image in your language of choice, I would reply that you type the appropriate syntax, the same way you type anything in Notepad++. If you have questions about the syntax, that is off topic here, because this Community is about the editor, not the language you happen to be typing with the editor: HTML questions belong in an HTML forum, not a text editor forum, and not the Notepad++ Community Forum in particular.
Hopefully one of those two will lead you in the right direction.